Preparation and thermal curing of single-ring bis(cyanate) ester monomers

ABSTRACT

A class of modified single-ring cyanate esters which have shown the ability to tailor and control the glass-transition (Tg) of the cured resins as well as the water uptake.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein may be manufactured and used by or forthe government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION

The invention generally relates to a class of modified single-ringcyanate esters which have shown the ability to tailor and control theglass-transition (Tg) of the cured resins as well as the water uptake.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing thermogravimetric analysis (TGA) of propyl3,5-bis(cyanato)benzoate under a nitrogen and air purge, according toembodiments of the invention.

FIG. 2 is a graph showing thermogravimetric analysis (TGA) of ethylhexyl3,5-bis(cyanato)benzoate under a nitrogen and air purge, according toembodiments of the invention.

FIG. 3 is a graph showing Differential Scanning Calorimetry (DSC)analysis of ethylhexyl 3,5-bis(cyanato)benzoate under a nitrogen purge.Heating rate of 10° C./min, according to embodiments of the invention.

FIG. 4 is a graph showing Differential Scanning Calorimetry (DSC)analysis of propyl 3,5-bis(cyanato)benzoate under a nitrogen purge.Heating rate of 10° C./min, according to embodiments of the invention.

FIG. 5 is a graph showing thermomechanical analysis (TMA) analysis ofethylhexyl 3,5-bis(cyanato)benzoate under a nitrogen purge. Heating rateof 10° C./min, according to embodiments of the invention.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not to be viewed as being restrictive of the invention, as claimed.Further advantages of this invention will be apparent after a review ofthe following detailed description of the disclosed embodiments, whichare illustrated schematically in the accompanying drawings and in theappended claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention generally relates to a class of modified single-ringcyanate esters which have shown the ability to tailor and control theglass-transition (Tg) of the cured resins as well as the water uptake.

No examples exist for making high performance composite resins fromrenewable resources (i.e. bioaromatics) in an efficient and costeffective manner. Phloroglucinol is a viable and cost effective sourceof bioaromatics (DRATHS corp. markets a bio-version). This work alsosolves the problem of water uptake in cyanate ester resins by tailoringthe structure of the monomer in a systematic and unprecedented manner.See attached disclosures included in this application.

The NAVY often works in wet humid environments. The NAVY and DoD alsoare accelerating weapons faster and flying them faster (i.e.hypersonics/kinetic weapons). The need for new high performance (HP)composite resins that do not suffer from “water issues” will provide adistinctive advantage to NAVY weapon platforms. This work isparticularly important for the NAVY since it addresses and solves theproblem of performance knock downs due to moisture uptake in compositematerials and provides a tougher better high performance compositeresin.

By inventing this new class of modified single-ring cyanate esters wehave shown the ability to tailor and control the glass-transition (Tg)of the cured resins as well as the water uptake. Examples have been madethat show a remarkably low water uptake and had no drop in the wet Tg asshown in Table 1. This is unusual and a very desirable property. Inaddition, the monomers can be made from sustainable and renewablebioaromatic feedstocks.

Data in Table 1 shows how by changing the ester group from propyl toethylhexyl (EH) we dramatically lower the water uptake from 2.93 wt-%(propyl ester) down to 0.83 wt-% EH ester. This is a dramatic andunprecedented lowering in water uptake for a pure hydrocarbon basedcyanate ester resin.

TABLE 1 Data for cured cyanate esters based on 3,5-bis(cyanate)benzaoateesters. EH is used as an abbreviation for (2-ethylhexyl). Dry Loss DryTan FC Loss FC Tan Wet Wet Tan Cure Water CTE Peak Delta Peak Delta LossDelta Enthalpy Uptake Sample (ppm/° C.) (° C.) (° C.) (° C.) (° C.) Peak(° C.) (° C.) (J/g) (wt %) EH Ester 127 (50° C.) 150 155 151 155 148 149614 0.83 Propyl 91 (150° C.) 224 229 206 213 159 171 790 2.93 Ester

Further data to support the unexpected and desirable manner by which thephysical properties of the bis(cyanate) monomer and that of the curedresins are shown in FIGS. 1-5. FIGS. 1 and 2 show that by having alarger alkyl group leads greater weight loss at high temperature, not anunexpected result. FIGS. 3 and 4 show each fully cure after one cycle inthe DSC instrument. In FIG. 5 we see the unexpected result that we Tgfor the cured resin is not affected by water. This is a truly astoundingdocumented result for these novel resins.

Embodiments of the invention generally relate to methods for preparing3,5-bis(cyanato)benzoate esters including, preparing a mixture3,5-dihydroxybenzoic acid and at least one alcohol, heating the mixturein the presence of an acid catalyst, removing unreacted alcohol bydistillation, purifying the 3,5-dihydroxybenzoate ester (I) from themixture,

treating the ester (I) with cyanogen halide in the presence of at leastone base and at least one solvent, isolating a 3,5-bis(cyanato)benzoateester (II) from the treated ester (I),

and purifying the 3,5-bis(cyanato)benzoate ester (II) to attain acyanate ester monomer capable of forming thermally cured resins.

Other embodiments of the invention generally relate to methods forpreparing 3,5-bis(cyanato)benzoate esters including, preparing a mixture3,5-dihydroxybenzoic acid and at least one amine, heating the mixture inthe presence of an acid catalyst, purifying said 3,5-dihydroxybenzamide(III) from the mixture,

treating (III) with cyanogen halide in the presence of at least one baseand one solvent, isolating the 3,5-bis(cyanato)benzamide (IV) from thetreated (III),

and purifying the 3,5-bis(cyanato)benzamide (IV) to attain a cyanateester monomer capable of forming thermally cured resins.

Embodiments of the invention generally relate to methods for preparing3,5-bis(cyanato)benzoate esters including, reacting3,5-di(benzyloxy)benzoic acid with oxalyl chloride, treating theacid/chloride with an alcohol in the presence of a base to form (V),

dissolving the (V) in at least one solvent, adding a solid catalyst andhydrogen gas, and reacting by stirring for about 2 to about 48 hours,removing of the catalyst by filtration and solvents by evaporationforming 3,5-dihydroxybenzoate ester (I), purifying the3,5-dihydroxybenzoate ester (I),

-   -   treating the 3,5-dihydroxybenzoate ester (I) with cyanogen        halide in the presence of at least one base and at least one        solvent forming 3,5-bis(cyanato)benzoate ester (II), isolating        the 3,5-bis(cyanato)benzoate ester (II), and purifying the        3,5-bis(cyanato)benzoate ester (II) to attain a cyanate ester        monomer capable of forming thermally cured resins.

In embodiments, the alcohol is an aliphatic alcohol having 1 to about 24carbons. In other embodiments, the alcohol is an aliphatic alcoholhaving 1 to about 24 carbons and including at least one fluorine atom.In yet other embodiments, the alcohol is both aliphatic and aromatic incomposition having a total of about 5 to about 24 carbons. Inembodiments, the aromatic includes at least one fluorine atom and atotal of about 5 to about 24 carbons. In embodiments, the halide isselected from the group consisting of bromide, chloride, and iodide. Inembodiments, the amine is an aliphatic amine having 1 to about 30carbons. In embodiments, the amine is an aliphatic amine having 1 toabout 30 carbons and includes at least one fluorine atom. Inembodiments, the amine is both aliphatic and aromatic in compositionhaving a total of about 5 to 30 about carbons. In embodiments, thearomatic includes at least one fluorine atom and a total of about 5 toabout 30 carbons.

In embodiments, said halide is selected from the group consisting ofbromide, chloride, and iodide. Embodiments further include thermalcuring of said 3,5-bis(cyanato)benzoate esters (II) to form compositeparts with low water uptake. Embodiments further include thermal curingof said 3,5-bis(cyanato)benzamides (IV) to form composite parts with lowwater uptake. Embodiments further include thermal curing of a mixture ofsaid 3,5-bis(cyanato)benzoate esters (II) and 3,5-bis(cyanato)benzamides(IV) to form composite parts with low water uptake where (II) can befrom 1 to 99% of the mixture. In embodiments, the base is selected froman aliphatic amine including from about 3 to about 18 carbons. Inembodiments, the base is an amine supported on cross-linked polymericsupport. In embodiments, the oxalyl chloride is used as 1.0 to 1.5mol-equivalent to the 3,5-di(benzyloxy)benzoic acid. In embodiments, thehydrogenation catalyst uses at least one metal selected from palladiumand platinum. In embodiments, the palladium is supported on a carbon. Inembodiments, the platinum oxide is the catalyst used in 0.01 to 2 wt-%of said 3,5-di(benzyloxy)benzoate ester (V).

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

While the invention has been described, disclosed, illustrated and shownin various terms of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

What is claimed is:
 1. A method for preparing 3,5-bis(cyanato)benzoateesters, comprising: reacting 3,5-di(benzyloxy)benzoic acid with oxalylchloride; treating said acid/chloride with an aliphatic and/or aromaticalcohol (ROH), wherein R is an aliphatic and/or aromatic component ofsaid aliphatic and/or aromatic alcohol, in the presence of a base toform (V):

dissolving said (V) in at least one solvent, adding a solid catalyst andhydrogen gas, and reacting by stirring for about 2 to about 48 hours;removing of said catalyst by filtration and solvents by evaporationforming 3,5-dihydroxybenzoate ester (I); purifying said3,5-dihydroxybenzoate ester (I); treating said 3,5-dihydroxybenzoateester (I) with cyanogen halide in the presence of at least one base andat least one solvent forming 3,5-bis(cyanato)benzoate ester (II);isolating said 3,5-bis(cyanato)benzoate ester (II): and purifying said3,5-bis(cyanato)benzoate ester (II) to attain a cyanate ester monomercapable of forming thermally cured resins.
 2. The method according toclaim 1, wherein said base is selected from an aliphatic amine includingfrom about 3 to about 18 carbons.
 3. The method according to claim 1,wherein said base is an amine supported on cross-linked polymericsupport.
 4. The method according to claim 1, wherein said oxalylchloride is used as 1.0 to 1.5 mol-equivalent to said3,5-di(benzyloxy)benzoic acid.
 5. The method according to claim 1,wherein said hydrogenation catalyst uses at least one metal selectedfrom palladium and platinum.
 6. The method according to claim 5, whereinsaid palladium is supported on a carbon.
 7. The method according toclaim 5, wherein said platinum oxide is the catalyst used in 0.01 to 2wt-% of said 3,5-di(benzyloxy)benzoate ester (V).